Device for compensating for hydraulic effective pressures
A device for compensating for hydraulic effective pressures in a hydraulic accumulator (9) and a hydraulic actuator (5) of a hydraulic system (11, 13) has a valve arrangement (27) for blocking a connection between the hydraulic actuator (5) and hydraulic accumulator (9) and has a control valve device (11) performing a pressure compensation when a predetermined difference in effective pressures is exceeded.
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The invention relates to a device for compensating for hydraulic effective pressures in a hydraulic accumulator and a hydraulic actuator of a hydraulic system.BACKGROUND OF THE INVENTION
In prior art hydraulic systems in which hydraulic actuators are used, for example, for support or lifting systems, hydraulic accumulators as spring or damper elements are hydraulically coupled to the actuator for cushioning or attenuating the movements of components moved by the hydraulic actuator. In some operating situations of such systems, however, an uncushioned, rigid dynamic connection between the actuator and the device actuated thereby is necessary, for example, for a hydraulically actuated boom intended to form a rigid support element, or for a tool to be controlled vibration-free when in use. In view of these requirements, the connection between the pertinent actuator and the hydraulic accumulator must be blocked.
In operation with the spring system blocked, the effective pressure in the hydraulic actuator changes according to the performance to be delivered by it. If at this point the system is transferred from the state of the blocked spring system back into the state with the hydraulic accumulator connected, a difference in the effective pressure between the hydraulic accumulator and the actuator leads to uncontrolled motion at the actuator. This uncontrolled motion poses a hazard to the system and a safety risk for system operators.SUMMARY OF THE INVENTION
An object of the invention is to provide a device that prevents this safety risk from uncontrolled motion.
This object is basically achieved according to the invention by a pressure compensation device having a valve arrangement that blocks the connection between the hydraulic actuator and the hydraulic accumulator. The valve arrangement has an additional control valve that affects pressure compensation when a predetermined difference of the effective pressures is exceeded. This pressure compensation avoids the risk of uncontrolled motion when the system is transferred from the state of the blocked spring system into the state with the spring system released, because the respective effective pressures of the hydraulic accumulator and of the hydraulic actuator are matched to one another.
If, in the state of the blocked spring system, the pressure that is effective in the hydraulic accumulator is less than the effective pressure in the respective working situation in the hydraulic actuator, pressure compensation can easily take place in the conventional manner by the hydraulic actuator charging the hydraulic accumulator via a non-return valve up to a constant pressure. The non-return valve closes when the pressure is equal.
The particular advantage of the invention is that, when a higher pressure prevails in the hydraulic accumulator, this pressure is reduced by pressure drainage toward the tank side of the hydraulic system.
The valve arrangement can have a directional valve that, in its release state, establishes a direct fluid connection between the hydraulic actuator and the hydraulic accumulator and interrupts this fluid connection in its blocked state. The control valve can be activated depending on the transfer of the directional valve into the blocked state and can contain a drainage valve controllable by a difference of effective pressures that exceeds the preset value into the drainage valve release state in which a drainage path that reduces the pressure difference toward the tank side of the hydraulic system is formed. This arrangement ensures that the equalization of the effective pressures takes place not only by charging of the hydraulic accumulator, but that charging of the hydraulic accumulator can take place only up to a pressure level at which the prescribed pressure difference is not exceeded, because, when this pressure difference is reached, pressure compensation takes place via the drainage valve toward the tank side of the system.
The hydraulic actuator can have at least one lifting cylinder of a machine with a piston side producing the lifting force and with a rod side connected to a control block of the machine. The piston side of the lifting cylinder is connectable via the directional valve to the hydraulic accumulator. The control valve has a connection to the hydraulic accumulator and fluid paths to the piston side and to the rod side of the lifting cylinder. Two fluid paths contain non-return valves that clear the fluid path only to the side of the lifting cylinder carrying the higher effective pressure.
A drainage valve can be in the form of a pressure compensator. In the release state, the pressure compensator clears the drainage path toward the tank side from the connection to the hydraulic accumulator and from the fluid path cleared in each case and leading to the lifting cylinder.
To avoid generating noise or causing damage to the hydraulic accumulator, the drainage process can take place from the accumulator to the tank side only when the pressure difference is somewhat greater than zero. At the same time, preloading that intensifies the action of the closing pressure can be active on the pressure compensator.
The pressure compensator can have a slide valve piston that, for its displacement into the blocking position on one piston area, can be loaded both with the closing pressure from the hydraulic working circuit and loaded with the force of a preload spring.
Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.
Referring to the drawings which form a part of this disclosure:
As mentioned, in certain operating situations a spring system is not useful or is detrimental. When a shovel 3 of a loader 1 is actuated, for example, spring compression or rebound has a negative effect on the accuracy of the positioning of the shovel 3. The system is transferred into the state of the blocked spring system such that, by supplying a hydraulic control pressure via a control line 50, the directional valve 27 is moved into the blocking state against the preload 29, as detailed below.
Another control port 47 of the drainage valve 37, referred to as the first control port, is connected via a control valve 49, when it is in its opening state shown in
With the released spring system in the state of
In the state shown in
The higher effective pressure of the hydraulic accumulator 9 is on the first control port 47 of the drainage valve 37 via the control valve 49 that is opened by the spring preload 52 and that is not energized. The second control port 35 carries the lower effective pressure of the input 17 via the line branch 31.
As already mentioned, the drainage valve 37 has a pressure compensator shown symbolically in
In the state depicted in
Advantageously, the opening pressure difference dictated by the piston geometry and the preload force 67 can be a pressure level of approximately 8 bar.
To ensure that the pressure present on the input port 53 does not take effect as the effective control pressure that determines the behavior of the pressure compensator, the piston area 73 indicated in
The piston 65 in
The invention thus ensures that the safety function is pressure compensation for all operating modes. The construction of the drainage valve 37 as shown in
1. A device compensating hydraulic effective pressures in a hydraulic accumulator and a hydraulic actuator of a hydraulic system with at least one lifting cylinder, comprising:
- a directional valve being movable between a blocked state thereof interrupting a fluid connection between a hydraulic actuator and a hydraulic accumulator and a release state thereof providing a direct fluid connection between said hydraulic actuator and said hydraulic accumulator for pressure compensation when a pre-determined value of a difference of effective pressures is exceeded;
- a control valve arrangement having an accumulator line leading from said directional valve to said hydraulic accumulator, having a first line branch leading from a piston side of a lifting cylinder to said directional valve and having a second line branch leading from a rod side of said lifting cylinder to said directional valve;
- a drainage valve of said control valve arrangement being blockable by the difference of effective pressures exceeding the pre-determined value to a release state thereof in which a drainage path reduces the pressure difference to a tank side of a hydraulic system; and
- a fluid path to said accumulator line bypassing said directional valve in blocked states of said first and second line branches, said fluid path having a non-return valves therein directed toward said piston side such that pressure from said piston side can be cleared via said fluid path by opening the non-return valve by an effective pressure exceeding pressure in the hydraulic accumulator and via said accumulator line to said hydraulic accumulator.
2. A device according to claim 1 wherein
- said lifting cylinder is on a machine, with said piston side producing a lifting force and with said piston side and said rod side being connected to a control block of said machine.
3. A device according to claim 1 wherein
- said drainage valve comprises a pressure compensator that clears said drainage path leading to said tank side from said accumulator line to said hydraulic accumulator and from said fluid path leading to said lifting cylinder that has been cleared in a release state thereof.
4. A device according to claim 3 wherein
- said pressure compensator comprises an input port connected to said hydraulic accumulator, an output part connected to said tank side, a first control port for supplying unblocked pressure and a second control port for supplying closing pressure.
5. A device according to claim 4 wherein
- said second control port is connected to said piston side in fluid communication.
6. A device according to claim 4, wherein
- a preload amplifies action of said closing pressure supplied to said second control port on said pressure compensator.
7. A device according to claim 4 wherein
- said pressure compensator comprises a slide valve piston displaceable into a blocking position on one piston area loadable with the closing pressure prevailing on said second control port and with a force of a preload spring, and comprises another piston area loadable with the unblocking pressure prevailing on said first control port.
8. A device according to claim 7 wherein
- said slide valve piston comprises an effective piston area bordering said second control port and being greater than an effective piston area bordering said first control port.
9. A device according to claim 7 wherein
- said input port of said pressure compensator is on an end of said slide valve piston opposite said preload spring and is formed by an axial end-side opening of a spool housing; and
- a control edge is on each of an end region of said slide valve piston and said spool housing between said end-side opening and said first control port, said first control port being offset axially to an inside of said spool housing.
10. A device according to claim 4 wherein
- a control valve in an opening state thereof connects said fluid path conveying the higher effective pressure to said first control port of said pressure compensator and delivering hydraulic pressure to said directional valve for movement to the blocked state thereof.
11. A device according to claim 1 wherein
- said directional control valve is mechanically preloaded into the release state thereof and is hydraulically movable into the blocked state thereof.
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Filed: Oct 16, 2009
Date of Patent: Apr 28, 2015
Patent Publication Number: 20110197573
Assignee: Hydac System GmbH (Sulzbach/Saar)
Inventor: Rüdiger Honsbein (Lebach-Dörsdorf)
Primary Examiner: Dwayne J White
Assistant Examiner: Logan Kraft
Application Number: 12/998,341
International Classification: F16D 31/02 (20060101); F15B 1/02 (20060101); E02F 9/22 (20060101);